PURPOSE: To shorten a processing time with a disk controller by performing simultaneously the transfer of data to a disk device and the transfer of data to a main memory.

CONSTITUTION: The parity check circuits 12-15 perform the parity check of the data stored in the sector buffers 1 and 2 which store the data equivalent to one sector respectively as well as the data stored in the additional sector buffers 3 and 4 which are set opposite to the buffers 1 and 2 and store the same data as those of buffers 1 and 2. Then the comparators 16 and 17 perform the comparison between the data stored in the buffers 1 and 2 and the data stored in the buffers 3 and 4. Based on the result of said comparison, the selectors 18 and 19 select the data of the buffers 1 and 2 or the data of the buffers 3 and 4 and transfer the selected data to a main memory. As a result, the transfer of data to a disk device is carried out simultaneously with the transfer of data to the main memory. Thus the processing time is shortened with the small circuit value.